1. Field of the Invention
The present invention relates to an image processing apparatus that determines whether a reading target original document is color or monochrome, a control method therefor, and a program.
2. Description of the Related Art
In an image processing apparatus using a color laser beam printer, it is desirable to execute copying using only black with respect to a monochrome original document, in consideration of the life of a drum and the amount of toner consumption. Accordingly, image processing apparatus are provided with the ACS (Auto Color Select) function for identifying whether an original document image is a color original document or a monochrome original document.
In such an image processing apparatus, when performing ACS determination on an original document read by an ADF (automatic document feeder), if ACS determination is performed with respect to a range wider than the width of the original document, there are cases where incorrect determination is performed. For example, there are cases where if color misalignment exists in the end portion of the original document, it is incorrectly determined that the original document is a color original document although the read original document is a monochrome original document.
In view of this, in order to correctly determine whether the original document that is read is a color original document or a monochrome original document, a technique has been proposed in which the width of the original document is specified using an original document width detection guide, a width narrower than the specified width of the original document is decided to be used as an ACS determination area, and then ACS determination is performed. Further, Japanese Patent Laid-Open No. 2002-199239 proposes a technique in which, in order to improve the original document reading position accuracy in ACS determination, a threshold value for determining a group of pixels to be color pixels in an original document that has been read is changed for each apparatus.
However, the above conventional techniques have the following problems. In order to accurately determine whether an original document is a color original document or a monochrome original document, it is desirable to make the above determination area used for ACS determination as large as possible, in the range where color misalignment in the end portion of the original document is not incorrectly detected. However, when attempting to make the ACS determination area as large as possible according to the size of the original document, it is necessary to provide a mechanism to detect the original document size, such as a guide that detects the width of the original document, in order to specify the original document size. If such a mechanism is mounted in an apparatus, the guide is necessary, thus increasing the size of the apparatus, and resulting in an increase in cost.
Further, in order to specify the original document size, although it is conceivable to have a user input the size of the original document in advance, this places a burden on the user. Also, in another case, the original document is scanned once in order to specify the size of an original document, and thereafter scanned again so as to read the image thereon, and although the accuracy improves in this case, there is the problem that productivity falls.